12.3. Understanding LVM

LVM (Logical Volume Management) partitions provide a number of
advantages over standard partitions. LVM partitions are formatted
as
physical volumes. One or
more physical volumes are combined to form a
volume group. Each volume
group's total storage is then divided into one or more
logical volumes. The logical
volumes function much like standard partitions. They have a file
system type, such as ext3, and a mount point.

The /boot Partition and LVM

The boot loader cannot read LVM volumes. You must make a
standard, non-LVM disk partition for your /boot partition.

To understand LVM better, imagine the physical volume as a
pile of blocks. A block is simply a
storage unit used to store data. Several piles of blocks can be
combined to make a much larger pile, just as physical volumes are
combined to make a volume group. The resulting pile can be
subdivided into several smaller piles of arbitrary size, just as a
volume group is allocated to several logical volumes.

An administrator may grow or shrink logical volumes without
destroying data, unlike standard disk partitions. If the physical
volumes in a volume group are on separate drives or RAID arrays
then administrators may also spread a logical volume across the
storage devices.

You may lose data if you shrink a logical volume to a smaller
capacity than the data on the volume requires. To ensure maximum
flexibility, create logical volumes to meet your current needs,
and leave excess storage capacity unallocated. You may safely grow
logical volumes to use unallocated space, as your needs dictate.

LVM and the Default Partition Layout

By default, the installation process creates / and swap partitions within LVM
volumes, with a separate /boot partition.